1. Field of the Invention
The present invention is generally concerned with the field of electroluminescent light emission devices and relates, in particular, to an electroluminescent light emission device according to the preamble of patent claim 1, which can be used as a white light source.
2. Description of the Related Art
In the past, various concepts have been developed in the endeavor to replace conventional white light sources based on incandescent or halogen lamps.
The furthest advanced concept is based on a semiconductor LED based on GaN or InGaN, which is at least partly embedded in a transparent casting resin material containing a converter substance for an at least partial wavelength conversion of the light emitted by the LED. In this case, the LED preferably has a plurality of light-emitting zones which generate a relatively broadband light emission spectrum above the emission spectrum of the converter substance in energy terms. The light in the blue or UV wavelength range emitted by the GaN-LED is at least partly converted by the converter substance into light having a wavelength in the yellow spectral range upon passing through the casting resin composition, so that white light is generated by additive color mixing. On the basis of this concept, small-format luminous sources such as torches and the like have recently been introduced commercially. However, these products still have various disadvantages. First of all, the spectral light emission curve of these white light sources is still not optimal, so that the physiological-optical impression of a white light source is in many cases not provided—at least not from all viewing angles. Furthermore, the luminous intensity of the white light sources which can be produced according to this concept is limited on account of the still excessively low light power of the GaN-LEDs and the necessary light conversion. Therefore, large-area white light sources having a high luminous intensity are not expected in the near future on the basis of this concept. A further concept for producing white light sources is based on the monolithic integration of a plurality of semiconductor layers and corresponding pn junctions on a substrate, the semiconductor materials being composed such that light having different wavelengths is generated in the pn junctions through current injection. U.S. Pat. No. 6,163,038 describes such a white light source based on the GaN material system. Two embodiments describe components in which a semiconductor layer sequence with three pn junctions is produced, which emit light having wavelengths of the complementary colors red, green and blue, thereby bringing about the optical effect of a white light source. This concept has the advantage that, in principle, polychromatic light of any desired color can be generated, thus resulting in a multiplicity of applications in the area of display and illumination devices. However, even with components of this type, it will not be possible to produce large-area illumination devices having a high luminous intensity with a tenable outlay in respect of costs.
A further concept for white light sources is based on organic light-emitting diodes (OLED), which have developed rapidly in recent times and are already used commercially in display devices of motor vehicles. Organic light-emitting diodes can generate white light relatively simply, since, by virtue of the great diversity of organic substances, different emitters can be brought together in order to generate white light. The published German patent application DE 199 16 745 A1 describes a light-emitting diode with organic light-emitting substances for generating light with mixed colors, in which a layer containing organic light-emitting substances is arranged between two electrode layers and two substrate carriers, in which case one of the carriers may be formed by a diffusing screen. The organic light emitter layer has a strip structure in which at least two types of strips are arranged alternately and strips of one type in each case having organic light-emitting substances which emit light of a specific color, strips of one type being driven jointly. The organic light-emitting substances of the two or three strip types are chosen such that, given suitable driving, the mixing of the radiated light of the strips produces white light. However, one disadvantage of the component described in the embodiment is that the width of the strips of the light emitter layers is so small that the strip structure can no longer be resolved upon normal observation by the human eye, as a result of which the production of the component becomes relatively complicated.